This invention relates generally to rotating machinery, and, more particularly, to a method and apparatus for testing a rotating shaft for desired characteristics.
Rotating machinery is often subjected to tests before leaving a manufacturing plant. For example, in one type of rotating machinery, such as electric motors with rotating output shafts, in addition to meeting electrical characteristic specifications, a specified shaft configuration is often required by customers for a selected application. Desired shaft configurations include the presence of a coupling feature, such as, for example, a flat or a keyway, and a selected direction of rotation of the shaft, i.e., clockwise or counterclockwise rotation. Another item of interest is the speed of the motor, i.e., the speed of rotation of the output shaft. Rotating machinery manufacturing plants typically include automated testing equipment to ensure that assembled products meet these and other customer requirements.
Present automated final motor testing equipment of high volume manufacturing plants typically include a wheel mechanism coupled to a computer system. The wheel mechanism contacts the motor shaft surface, generating signals for analysis by the computer system to determine the direction of rotation of the shaft. An accelerometer is coupled to the wheel mechanism and detection circuitry generates a filtered representation of the amplitude of a signal from the accelerometer. By analyzing the signal amplitude, the computer system determines the presence or absence of a shaft coupling feature during a motor start test at full or reduced voltage.
Contact testing of the motor shaft, however, is disadvantaged in several aspects. For example, the wheel or contact mechanism tends to wear during high volume testing of motors, which affects the calibration and frequency response characteristics of detection circuitry. Also, when using fast cycling test sequences, the startup test may be completed too quickly for the filtered vibration signal to establish a reliable amplitude level to determine the absence of a shaft coupling feature.
Accordingly, it would be desirable to provide a longer life motor shaft testing apparatus and method for application in high volume motor testing that is less susceptible to calibration effects over time and that may be reliably used even when fast cycling techniques are employed.
In an exemplary embodiment of the invention, a motor shaft testing apparatus for non-contact testing of a rotating motor shaft includes a first proximity sensor coupled to an automated motor test system. The automated motor test system includes a microprocessor and circuitry adapted for at least one of a digital multimeter function and an oscilloscope function for analyzing an output signal form the first proximity sensor to determine the presence or absence of a coupling characteristic, such as a flat, on a given motor shaft oriented proximally to the first proximity sensor.
More specifically, the automated test system generates a first waveform corresponding to the first signal. Through comparative evaluation of the generated signal and predetermined threshold values, such as, for example, comparing an amplitude of the waveform with an empirically determined amplitude to detect the presence of the coupling characteristic on the shaft, a non-contact testing apparatus is provided that reliably detects shaft coupling characteristics.
In other aspects of the invention, shaft speed may also be detected by determining a pulse frequency of the output signal of the first proximity sensor, and, with the addition of a second proximity sensor generating a second output signal, a phase relationship between output signals of the first and second proximity sensors is determined, thereby indicating a direction of rotation of the shaft.